Apparatus and method for analyzing a body fluid

ABSTRACT

A method and apparatus (10) for determining the remission of a chemistry (106) which reacts with a medically significant component of a body fluid. The remission of the chemistry (106) changes as it reacts. The method and apparatus (10) include irradiating the chemistry (106) with a radiation source (182), detecting remissions of radiation from the chemistry (106) with a radiation detector (300), providing a radiation pathway (164) between the source (182) and the chemistry (106), providing a remission pathway (164) between the chemistry (106) and the detector (300), and detecting the rate of change of remission of the chemistry (106) with respect to time. The irradiating, detecting and rate detecting steps and apparatus comprise initially irradiating the chemistry (106) at a first time rate and detecting remissions therefrom, comparing remission data from remission readings spaced apart by a first number of intervening remission readings, and determining when the difference between compared readings exceeds a first predetermined limit. The time rate of irradiation of the chemistry is changed once the difference between compared readings exceeds the first limit. Remission data from remission readings spaced apart by a second number of intervening remission readings are then compared. The method and apparatus next determine when the difference between compared readings no longer exceeds a second predetermined limit. The last remission reading is then converted to the concentration of the medically significant component of the body fluid.

BACKGROUND OF THE INVENTION

This invention relates to apparatus and methods for reading theconcentration of a medically significant component of a biological fluidfrom a test strip. It is disclosed in the context of an apparatus and amethod for reading the concentration of glucose in blood reacted on atest strip with a chemistry with which the strip has previously beentreated.

The difficulty many people have with preparing test strips treated withchemistries with bodily fluids such as blood and urine is known. Manyusers of such strips have poor eyesight owing to diabetes, to age, andto other causes as well. Many users have reduced dexterity or strengthin their hands owing to age and to other causes. Frequently these causesare the reasons why these users are testing their bodily fluids for, forexample, glucose concentration to begin with.

The problems with such strips only begin with dosing the strips with thebodily fluid or fluids to be analyzed. The chemistries are reactantswith the medically significant component(s) of the fluids. Thesereactants react with the medically significant component(s) resultingtypically in some colorimetric indication of the concentration of themedically significant component of the fluid. However, these reactionscontinue, typically for extended times, until all of the reactants havereacted. Consequently, it is generally necessary to time the reaction ofthe medically significant component with the strip chemistry so that acolorimetric comparison of the reacted strip chemistry to a standard ona color chart can be made at some established time after the reaction isinitiated by depositing the fluid on the strip. Otherwise, if thereaction is not permitted to proceed long enough, or is permitted toproceed too long, the color corresponding to the extent of the reactionwill not match the correct standard on the chart.

In addition to potential problems with how long the chemistry on thestrip and the medically significant component of the body fluid arepermitted to react, there are problems with many of such chemistrysystems with how much of the body fluid is applied to the strip, sinceincorrect amounts of the reactants may affect the validity of the testas adversely as errors in the timing of the reaction. Either way, afalse reading, sometimes with dire consequences, will result.

The present invention makes use of an endpoint chemistry system of thetype described in U.S. Pat. No. 4,929,545. The disclosure of U.S. Pat.No. 4,929,545 is incorporated herein by reference. The advantages of anendpoint chemistry are clear. For the user who frequently has pooreyesight and/or manual dexterity, there is no need to be concerned abouthow long the reaction has proceeded. The reaction reaches an endpoint inrelatively short order after which there is no significant shift in thecolor of the reaction products on the strip. In addition, thearchitecture of the strip described in U.S. Ser. No. 07/661,788, filedFeb. 27, 1991, IMPROVED TEST STRIP, naming as inventors McCroskey,Freitag, Smith, Dean, Secrest and Bouse, and assigned to BoehringerMannheim Corporation, is such that the proper dose of the body fluid,the biologically significant component of which is to be reacted withthe chemistry on the strip, will always be available for the reaction.Any excess is wicked away from the reaction site by the striparchitecture. Thus, all the user need do is be sure enough of the bodilyfluid is present at the reaction site on the strip to react with thechemistry with which the strip is treated. The disclosure of U.S. Ser.No. 07/661,788 is incorporated herein by reference.

SUMMARY OF THE INVENTION

According to the invention, a method and apparatus are provided fordetermining the remission of a chemistry which reacts with a medicallysignificant component of a body fluid. The remission of the chemistrychanges as it reacts. The method and apparatus include irradiating thechemistry with a radiation source, detecting remissions of radiationfrom the chemistry with a remission detector, providing a radiationpathway between the source and the chemistry, providing a remissionpathway between the chemistry and the remission detector, and detectingthe rate of change of remission of the chemistry with respect to time.The irradiating, detecting and rate detecting steps and means comprisethe step of and means for initially irradiating the chemistry at a firsttime rate and detecting remissions therefrom, the step of and means forcomparing remission data from remission measurements spaced apart by afirst number of intervening remission measurements, the step of andmeans for determining when the difference between compared data exceedsa first predetermined limit, the step of and means for changing the timerate of irradiation of the chemistry to a second and greater rate ofirradiation per unit time once the difference between compared dataexceeds the first limit, the step of and means for comparing remissiondata from remission measurements spaced apart by a second number ofintervening remission measurements, which second number may be the sameas, or different from, the first number, the step of and means fordetermining when the difference between compared data no longer exceedsa second predetermined limit, and the step of and means for convertingremission data identified based upon this determination to theconcentration of the medically significant component of the body fluid.

Illustratively, the first time rate, the first number of interveningremission measurements, the first predetermined limit, the secondpredetermined limit, and a conversion parameter for converting theremission data to the concentration are provided from a read only memory(ROM).

Illustratively, the invention further comprises the step of and meansfor providing a first current flow through a radiation sensitive devicein response to detection of remission. The first current flow dischargesa capacitor from a known, initial charged condition. A constant currentis provided for recharging the capacitor to the known, initial, chargedcondition when the first current flow terminates.

Additionally, illustratively the rate detecting step and means includethe step of and means for generating a time base, and the step of andmeans for measuring the time interval required for the constant currentsource to recharge the capacitor to the known, initial, chargedcondition.

Further illustratively the invention comprises the steps of and meansfor supporting the chemistry on a substrate, accepting the substrate ina device defining the pathway along which radiation is guided from theradiation source to the chemistry when the substrate is correctlyinserted into the device and the pathway along which remission is guidedfrom the chemistry to the remission detector when the substrate iscorrectly inserted into the device, a remission standard, means formovably supporting the remission standard to permit it to move from aposition in which it receives radiation from the radiation source andproduces a standard remission which is guided along the pathway to theremission detector when no substrate is inserted into the device to aposition separated from the radiation source by the substrate when thesubstrate is inserted into the device.

Additionally illustratively the invention further comprises the steps ofand means for irradiating the substrate with a second radiation sourceand detecting remissions from the substrate with a second remissiondetector, and providing a second pathway along which radiation is guidedfrom the second radiation source to the substrate when the substrate isinserted into the device and along which remission is guided from thesubstrate to the second remission detector when the substrate isinserted into the device.

Illustratively, the remissions detected by the first-mentioned andsecond remission detectors are detected substantially simultaneously.

Illustratively, the invention is incorporated into an instrument fordetermining the concentration of a medically significant component of abody fluid and for indicating the determined concentration of themedically significant component to a user of the instrument. Theinstrument comprises an instrument case for the instrument's componentsincluding the device. One of the instrument's components comprises aprinted circuit board for mounting at least a portion of the means formovably supporting the remission standard, the first-mentioned andsecond radiation sources and the first-mentioned and second remissiondetectors.

Further illustratively the case includes a socket for receiving a key onwhich the ROM is provided. Insertion of the key into the socket couplesthe ROM to the instrument and permits access by the instrument to theinformation contained in the ROM.

Illustratively, the pathway along which remission is guided from thechemistry to the remission detector when a substrate is correctlyinserted into the device includes a first slot. The pathway along whichremission is guided from the chemistry to the first-mentioned remissiondetector when a substrate is inserted into the device includes a secondslot formed in a first surface adjacent the first slot. A second surfacelies at a small, nonzero angle to the first surface. The pathway alongwhich radiation is guided from the source to the chemistry when thesubstrate is inserted into the device includes a third slot formed inthe second surface. The third slot lies between the source and thechemistry when the substrate is properly inserted into the device. Thefirst slot lies between the third slot and the chemistry when thesubstrate is properly inserted into the device. The first slot liesbetween the chemistry and the first-mentioned remission detector whenthe substrate is properly inserted into the device. The second slot liesbetween the first slot and the first-mentioned remission detector. Thesecond surface lies between the means for supporting the radiationsource and the chemistry when the substrate is properly inserted intothe device.

BRIEF DESCRIPTION OF DRAWINGS

The invention may best be understood by referring to the followingdetailed description and accompanying drawings which illustrate theinvention. In the drawings:

FIGS. 1-8 illustrate exploded perspective views, from various differentangles, of various components of an instrument constructed according tothe present invention;

FIG. 9 illustrates a partly block and partly schematic circuit diagramof the electric circuit of the instrument illustrated in FIGS. 1-8;

FIG. 10 illustrates a type of flow diagram useful in understanding theoperation of the instrument illustrated in FIGS. 1-8;

FIG. 11 illustrates a % remission versus time curve useful inunderstanding the operation of the software of the instrument of FIGS.1-9; and

FIG. 12 illustrates another % remission versus time curve useful inunderstanding the operation of the software of the instrument of FIGS.1-9.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Referring now to FIGS. 1 and 8, an instrument 10 according to theinvention includes a case 12 having a front portion 14, a rear portion16, a key housing portion 18 and a strip carrier holder portion 20. Aprinted circuit board 22, the contents of which will be considered inmore detail in the discussion of FIG. 9, is sandwiched generally betweenthe front and rear portions 14, 16, respectively. Front portion 14includes a relief 24 of generally trapezoidal configuration at thecenter of which is a generally circular opening 26. A generally rightcircular cylindrical stem 28 extends downwardly from the underside offront portion 14 beneath opening 26. This stem 28 slidably receives astem 30 provided on the back of an ON/OFF button 32 of the same shape asrelief 24. The lower end of stem 30 is split axially and somewhatfrustoconical in configuration so that button 32 is captured in relief24 when stem 30 is pushed into opening 26 until the split, frustoconicalend 36 of stem 30 clears the bottom end 38 of stem 28. The portion ofstem 30 above end 36 is somewhat longer than stem 28 so that somemovement of button 32 vertically in relief 24 is possible.

Front casing portion 14 also includes a wall 40 inside of, and parallelwith, a region 42 of an end wall thereof. Wall 40 includes a verticallyextending groove 44 open at its bottom 46 and with a semicircular top48. A memory button 50 has ribs 52 on its back wall spaced apartslightly less than the width of groove 44. Button 50 excluding ribs 52is slightly thicker than the space between wall 40 and region 42. Theflexible resin construction of front portion 14 and a circular opening54 of slightly larger diameter than button 50 in region 42 permits thewall 40 to flex away from region 42 as button 50 is forced into thespace between them and snaps into place protruding through opening 54. Aflange 56 on button 50 keeps it from going all the way through opening54 and falling from front portion 14.

The front and rear portions 14, 16 include respective, cooperating,somewhat arcuate cutouts 60, 62 (FIGS. 1, 6 and 8), for key housingportion 18. Key housing portion 18 is designed to receive anelectronically readable information carrier, or key, 64 (FIG. 2) of thetype described in U.S. Pat. No. 5,053,199. The disclosure of U.S. Pat.No. 5,053,199 is incorporated herein by reference. Front and rearportions 14, 16 also include cooperating cutouts 68, 70 (FIGS. 1, 6 and8) for receiving the strip carrier holder portion 20. Front portion 14also includes a window 74 (FIGS. 1 and 8) around which a liquid crystaldisplay 76-supporting bezel 78 (FIGS. 3 and 7) fits on the inside offront portion 14. Bezel 78 mounts the LCD 76 so as to be visible throughwindow 74 and provides the necessary electrical connections 79 to LCD76.

The back portion 16 of the case 12 also includes means for mounting apiezoelectric beeper transducer 80 (FIG. 6) and for providing electricalcontact 81 thereto and a battery housing cutout 82 having a pivotallymounted door 84 for convenient insertion and removal of a six-voltbattery 86.

The lips 88, 90 of front and back portions 14, 16, respectively, arecomplementarily configured to snap together. As further insuranceagainst their inadvertently coming apart, a self tapping screw 92(FIG. 1) through back portion 16 and into a stem 94 molded on the insideof front portion 14 holds portions 14, 16 together. Screw 92 extendsthrough a hole 96 provided therefor in printed circuit board 22, which,along with the configurations of the interiors of front and backportions 14, 16, holds board 22 in place.

The strip carrier holder portion 20 includes an outer case portion 100provided with grooves 102 (FIG. 4) on its top and bottom surfaces to aidin gripping it and snapping it into and out of engagement with the front14 and back 16 case portions. Case portion 100 is provided with anopening 104 for inserting chemistry strips 106, the remissions of whichare to be read, into the instrument 10. The margins 108 of opening 104are somewhat funnel-shaped to assist in insertion of the strips 106 intothe instrument 10 in the correct orientation. A pair of somewhatpawl-shaped members 110 extend rearwardly of case portion 100 beneathopening 104. Members 110 define between them a slot 112 which opens intoa somewhat equilateral triangular region 114 near their remote ends 116,then closes back to its slot configuration, and then opens into asomewhat funnel shape 118 adjacent the remote ends 116 of members 110. Astrip carrier body 120 includes a lower web portion 122 along each ofthe opposite sides of which extend two guide ribs 124. Web portion 122is only slightly thinner than slot 112 is for most of its length. Guideribs 124 are spaced apart only slightly further than the verticalthickness of each of members 110. These dimensions permit strip carrierbody 120 to be slid into the slot 112 defined between members 110. Atriangular horizontal cross section projection 126 spaced an appropriatedistance along web portion 122 on each side thereof between guide ribs124 cooperates with region 114 on case portion 100 to lock strip carrierbody 120 between members 110.

Near its end remote from case portion 100, strip carrier body 120includes a pair of horizontally projecting ears 130, each of Which isprovided with an elongated slot 132. Slots 132 extend generallytransversely to the directions of motion of strips 106 as the strips areinserted into opening 104 and into the strip carrier holder 20 andremoved therefrom. A lift 134 includes a pair of vertically, oppositelyextending trunnions 136 which engage in respective slots 132 to permitlift 134 to move away from strip carrier body 120 as a strip 106 to beread is inserted therebetween. Lift 134, in turn, includes a pair orhorizontally extending ears 138 at its forward end opposite the end atwhich trunnions 136 are provided. Each ear 138 is provided with avertically extending circular cross section hole 140. A high reflectance(remission) white tile 142 is provided with a pair of trunnions 144 bywhich it is pivotally attached, by insertion of trunnions 144 intorespective holes 140, to lift 134. Directly across from the point 146 atwhich white tile 142 projects through an opening 150 provided thereforin lift 134, strip carrier body 120 is provided with a slot 152. Stripcarrier body 120 is also provided with another slot 154 between slot 152and case portion 100, and with a frustoconical relief 156 (illustratedonly in FIG. 1) on the side thereof opposite the side to which lift 134is attached.

An optics assembly 160 (FIGS. 1, 3 and 5) mounted on the printed circuitboard 22 cooperates with the strip carrier holder portion 20. Thecooperation of these two components negates any possible misalignmenterrors between the optics and the strips 106. This cooperation is aidedby the designs and tolerances of some of the molded plastics parts fromwhich the strip carrier holder portion 20 and optics assembly 160 arelargely constructed. These designs and tolerances permit the componentsof the strip carrier holder portion 20 and optics assembly 160 whichmust be properly aligned for accurate reading of the reacted strips'106s' remissions to align properly when the strip carrier holder portion20 is assembled into the instrument case 12.

Optics assembly 160 includes an optics housing 162. Housing 162 houses aleaf spring 168 and, across from spring 168, a wall 170 against whichthe spring 168 forces the strip carrier body 120 to position it and itsrelated components 134, 142 and a strip 106 carried thereby properlyrelative to the instrument 10's optics. A frustoconical projection (notillustrated) projecting toward spring 168 from wall 170 adjacent theinner end 171 of housing 162 engages relief 156 on strip carrier body120 when strip carrier body 120 is correctly positioned in opticshousing 162. A pair 174, 176 (FIG. 3) of transparent plastic prisms,molded as a single piece 177, are mounted on printed circuit board 22 inseparate internal regions 178, 180, respectively, (FIG. 5) of housing162. A light emitting diode 182 is mounted on board 22 and fitted intoan LED adapter 184 which, in turn, is fitted into an LED socket 186provided on housing 162. LED 182 is the initiation, or "upstream" end,of a glucose measurement channel.

Wall 170 is provided with a vertical slit opening 190 opposite theopening of socket 186 into housing 162. In the assembled optics assembly160, this slit opening 190 is directly adjacent prism 174, the smallerof the two prisms provided by piece 177. In order to avoid receiving thedirect reflected light from the reacted test chemistry on a strip 106,prism 174 is oriented at an angle to the surface of the strip 106 otherthan the angle of incidence of light from LED 182 onto, or the angle ofreflection of light from LED 182 from, strip 106. Illustratively, prism174 is oriented at an angle of about 77° to the surface of strip 106.This increases the likelihood that light received by prism 174 is notdirect reflected light, but rather ambient remission light, from thereacted chemistry on strip 106. This diffuse light is a better gaugethan direct reflected light of the end point of the reaction between theglucose in blood applied to strip 106 and the chemistry with which strip106 is treated. Thus, this ambient remission light is a better gauge ofthe concentration of the glucose content of the blood.

Prism 176 is oriented directly adjacent a slit opening 191 through wall170 in the assembled optics assembly 160. The problem of obtaining adiffuse or remission light component of the light reflected from strip106 is not so great with the light entering prism 176 as it is with thelight entering prism 174 because the light entering prism 176 is usedonly to determine whether there is a strip in strip carrier body 120,and, if so, whether the strip is properly oriented with its chemistryimmediately opposite opening 190 and prism 174. Since prism 176 is notin the chemistry reading channel 164, the remission reading from it isnot so critical.

Both of prisms 174, 176 have curved faces facing strip 106. These curvedfaces function as lenses to focus the light remissions entering theprisms on the devices which detect these remissions. The lensesincorporated into prisms 174, 176, in other words, have focal lengthsequal to the distances from the lenses to their respective regions ofinterest on the strip 106 and also equal to the distances from thelenses to their respective detector devices.

Turning now to FIG. 9, the operation of instrument 10 is controlled by amicrocomputer (μc) 200 such as the NEC type μPD75P308 μc. All subsequentreferences herein to pin and terminal numbers and names will be to thepin and terminal numbers and names of the specific integrated circuitsand other devices identified herein as exemplary. It is to beunderstood, however, that other integrated circuits may exist which areequally suited to provide the functions required by instrument 10. Theclock for μc 200 is a 4.19 MHz crystal 202 which is coupled acrossterminals X1-X2 thereof. The terminals of crystal 202 are also coupledthrough respective 33 pF capacitors to ground. The V_(DD) supply for μc200 is provided by a PNP transistor 204 such as a BC858C, the base ofwhich is coupled through a 62 KΩ resistor 206 to terminal P4.1 of μc200. The emitter of transistor 204 is coupled to positive batteryvoltage (+6VDC), hereinafter referred to as VBAT. V_(DD) appears at thecollector of transistor 204. The collector of transistor 204 is coupledto its emitter by the parallel combination of two 200Ω resistors. Thecathode of a diode 208 is coupled to the collector of transistor 204.The anode of diode 208 is coupled to ground. Diode 208 illustratively isa type 1N4148 diode.

The RESET terminal of μc 200 is coupled to the collector of a transistor210 and through a 10 KΩ resistor to V_(DD). The emitter of transistor210 is grounded. Its base is coupled through a 22K Ω resistor 212 to thejunction of a 0.l μF capacitor 214 and a 1 MΩ resistor 216. The otherterminal of capacitor 214 is coupled to VBAT. The other terminal ofresistor 216 is coupled to ground.

An electronic log book mode (ELB) connector 220 has three terminals. Afirst of these, 222, is coupled through a 10 KΩ resistor to terminals P3.0/LCDCL and P 0.0/INT4 of μc 200. Terminal 222 is also coupled toground through the parallel combination of a 680 pF capacitor and a 220KΩ resistor. Terminal 224 is coupled through a 10 KΩ resistor toterminal P3.2 of μc 200, and to ground through the parallel combinationof a 680 pF capacitor and a 220 KΩ resistor. Terminal 226 is coupled toground.

The eight terminals 231-238 of the key housing portion 18 are coupled,respectively, to: μc 200's terminal P7.3/KR7; μc 200's terminalP7.2/KR6; μc 200's P7.0/KR4; μc 200's terminal P6.3/KR3; ground; oneterminal of a 200 KΩ resistor 240, the remaining terminal of which iscoupled to terminal 234; nothing (blank); and terminal 236.

A number of variables exist which affect the reading of the reactedchemistry on a strip 106. For the reading to be as free of errors asinstrument 10 can make it, these variables must be accounted for to theextent possible by instrument 10 in the process of calculating the endpoint remission of the reacted chemistry. One of these variables ishumidity, and it is taken into consideration by a humidity sensor 242 ofstandard configuration coupled between ground and an input terminalP0.3/SI/SB1 of μc 200. Humidity sensor 242 is also coupled through a 1MΩresistor 244 and a 0.01 μF capacitor 246 to ground. VBAT is supplied tothe emitter of a PNP transistor 248, illustratively a BC858C. Thecollector of transistor 248 is coupled to key housing portion 18'sconnectors 236 and 238 and to the junction of resistor 244 and capacitor246.

An internal EEPROM 250 has its CS, SK, DI and DO terminals coupled,respectively, to the P7.1/KR5, P7.2/KR6, P7.0/KR4 and P6.3/KR3 terminalsof μc 200. The V_(CC) and ORG terminals of internal EEPROM 250 arecoupled to the collector of transistor 248. The GND terminal of internalEEPROM 250 is coupled to ground. Internal EEPROM 250 illustratively is acatalyst Semiconductor type CAT93C46 integrated circuit, as is theintegrated circuit in code ROM key 64.

A series string of an 8.2 KΩ resistor 252, a 10 KΩ resistor 254, a 10 KΩresistor 256, and a 10 KΩ resistor 258 is coupled between terminalP6.1/KR2 of μc 200 and ground. The junction of resistors 252, 254 iscoupled to terminals VLC.0. and BIAS of μc 200. The junction ofresistors 254 and 256 is coupled to terminal VLC1 of μc 200. Thejunction of resistors 256 and 258 is coupled to terminal VLC2 of μc 200.

Transducer 80 is coupled across terminal P2.3/BUZ of μc 200 and ground.A diode 260 is coupled across transducer 80 with its anode coupled toground and its cathode coupled to terminal P2.3/BUZ. Another diode 262has its anode coupled to terminal P2.3/BUZ and its cathode coupled toV_(DD).

The COM.0.-COM2 and DS1.0.-DS.0. terminals, respectively, of μc 200 arecoupled to respective terminals of the same names, pins 1-14, of LCD 76.

An infrared strip 106 sensor channel 166 includes an LED 264 and a lightsensitive transistor (LST) 266 separated by a partition in a commonhousing (not shown). The larger prism 176 is mounted on printed circuitboard 22 so that its bottom surface rests directly on the top surface ofthe housing in which LED 264 and LST 266 are housed. LED 264 and LST 266illustratively are a Toshiba type TLP908 integrated circuit. Light fromLED 264 shines upward through the bottom of the larger prism 176 and isreflected out through the lens of prism 176 onto the strip 106. Thereflected light returns through the lens and is reflected downwardwithin the prism 176 and out the bottom thereof where it is received byLST 266. The resultant conductivity of LST 266 corresponds to a certainpercentage remission of the light from LED 264. That percentageremission establishes whether a strip 106 is present in strip carrierbody 120 and, to an extent, whether that strip 106, if present, isproperly oriented.

The way the strip 106 and strip 106 orientation are detected is asfollows. Light returning in channel 166 to the base of LST 266 causes itto conduct. A current mirror including NPN transistors 268 and 270 inconventional current mirror configuration provides equal currentsthrough the collectors of these two transistors in response to currentflow in the emitter of LST 266. A 0.47 μF capacitor 272 is coupledacross the collector and emitter of transistor 270 and discharges at arate determined by the amount of light falling on the base of LST 266 towhich LST 266 is sensitive. This configuration subtracts from theinitial voltage across capacitor 272 the integral of the light fallingon the base of LST 266. Current is supplied to LED 264 for apredetermined, set period of time. The remission from strip 106 to thebase of LST 266 determines how deeply discharged capacitor 272 becomes.Capacitor 272 is then charged from a constant current source for aperiod of time which is measured using the system clock, until capacitor272 has recharged to some reference voltage. The length of the periodthat capacitor 272 takes to recharge to reference voltage is a period oftime, a number of strokes of the system clock, and converts to a digitalvalue the percentage remission of channel 166. This translates into thepresence or absence of a strip 106 in the strip carrier body 120 and, toan extent, its orientation in strip carrier body 120. The instrument 10,once it has established that a strip 16 is present in the strip carrierbody, next decides whether the strip 106 is properly oriented with itsreagent pad in front of slot 190 and prism 174, or whether the strip 106is backward or upside down. Of course, the strip architecture must besuch that different ranges of percentage remission readings arepresented for these different strip 106 orientations, and this is so.See U.S. Ser. No. 07/661,788.

To accomplish these objectives, the anode of LED 264 is coupled to VBATand its cathode is coupled to the collector of a transistor 276, whichillustratively is a type BC848C NPN transistor. The emitter oftransistor 276 is coupled through an 82Ω feedback resistor to ground.The base of transistor 276 is provided with periodic LED 264 drivesignals from terminal P5.1 of μc 200. The base of transistor 276 is alsocoupled through two diode-connected temperature compensation transistors280, 282 in series to ground. Transistors 268, 270, 280, 282illustratively are a type MC3346D quad transistor integrated circuit.The emitter of LST 266 is coupled to the collector and base of currentmirror transistor 268, and to the base of current mirror transistor 270.The collector and base of transistor 268 and the base of transistor 270are also coupled to terminal P5.0 of μc 200. The emitters of transistors268, 270 are grounded. The collector of transistor 270, in addition tobeing coupled to capacitor 272, is coupled to the inverting (-) inputterminal of a difference amplifier 286, and to the collector of a PNPtransistor 288 such as a type BC858C transistor. The output terminal ofdifference amplifier 86 is coupled to the P3.1/SYNC terminal of μc 200.The emitter of transistor 288 is coupled to terminal P5.3 of μc 200. Thebase of transistor 288 is coupled to the output terminal of a differenceamplifier 290.

The inverting (-) and non-inverting (+) input terminals of differenceamplifier 290 are coupled through a 20 KΩ resistor and a 150Ω resistor,respectively, to the collector of LST 266. A 5.l KΩ resistor is coupledfrom the base of transistor 276 to the collector of LST 266 as well. Thecollector of LST 266 is coupled to the + input terminal of a differenceamplifier 294, the - input terminal of which is coupled through a 150 KΩresistor to terminal P6..0.0/KRO of μc 200. The output terminal ofdifference amplifier 294 is coupled to terminal P3.3 of μc 200. The -input terminal of difference amplifier 294 is also coupled through a0.01 μF capacitor to ground.

Turning now to the mechanism and electronics by which the remission ofthe reagent pad portion of strip 106 is read when a strip 106 isproperly inserted into strip carrier body 120, LED 182 is the beginningof channel 164. The anode of LED 182 is coupled to VBAT and its cathodeis coupled to the collector of an NPN transistor 298. Transistor 298illustratively is a type BC848C transistor. The emitter of transistor298 is coupled through a 120Ω feedback resistor to ground. The base oftransistor 298 is coupled to terminal P5.2 of μc 200, and through a 20KΩ resistor to the + input terminal of difference amplifier 294. Theremission of the reagent pad of a strip 106 is supplied to a photosensor300, such as a Siemens type TFA1001W integrated photosensor. Photosensor300 is mounted in closely spaced relation to the bottom of the smallerprism 174 so that remissions from the chemistry region of strip 106 thatenter the lens surface of prism 174 are reflected down through it andexit from its bottom into photosensor 300.

Power for photosensor 300 is provided through a PNP transistor 302,which illustratively is a type BC858C transistor. The emitter oftransistor 302 is coupled to VBAT. Its base is coupled through a 62 KΩresistor to terminal P4.2 of μc 200. Its collector is coupled to groundthrough a 22 μF tantalum capacitor 304. The voltage VD1 across capacitor304 is coupled across terminals +VS and -VS of photosensor 300. A 0.01μF capacitor is also coupled across terminals +VS and -VS. The VSTAB andFCOMP terminals of photosensor 300 are joined through a 1MΩ resistor.The VSTAB terminal is also coupled to the + input terminal of adifference amplifier 308. The - input terminal of difference amplifier308 is coupled to its output terminal, making it a substantially unitygain amplifier. The output terminal of difference amplifier 308 is alsocoupled to the + input terminal of difference amplifier 294. Differenceamplifiers 286, 290, 294 and 308 illustratively are a type LM324A quaddifference amplifier integrated circuit.

Terminal P6.2/KR2 is coupled through a 200 KΩ resistor to the anode of adiode 310 which illustratively is a type IN4148. The cathode of diode310 is coupled to the INHIBIT terminal of photosensor 300. The conductorextending between the cathode of diode 310 and the INHIBIT terminal ofPhotosensor 300 is capacitively coupled through a 680Ω resistor toground and through a 360Ω resistor to the + input terminal of differenceamplifier 286. The + input terminal of difference amplifier 286 iscoupled through a 200Ω resistor to the + input terminal of differenceamplifier 290. The OUTPUT terminal of photosensor 300 is coupled tothe - input terminal of difference amplifier 286.

One terminal of an ON/OFF switch 312 operated by ON/OFF button 32 iscoupled to ground. The other terminal of ON/OFF switch 312 is coupled tothe P1.1/INT1 terminal of μc 200. The P1.2/INT2 terminal of μc 200 iscoupled to one terminal 316 of a memory switch 314 operated by memorybutton 50. Terminal 316 of memory switch 314 is coupled through a 220KΩresistor to ground. The other terminal of memory switch 314 is coupledthrough a 220KΩ resistor to the P1.1/INT1 terminal of μc 200.

The symbols which can appear on LCD 76 include numbers 00.0 through99.9, the indications mg/dL (milligrams per deciliter), mmol/L(millimoles per liter), mem (which stands for memory), a battery icon,an icon of a blood droplet being deposited on a strip, the word code,and an error icon, a box with an "X" through it, each quadrant of thebox being capable of being separately energized.

Referring now to FIG. 10, the instrument 10 is turned on by depressingON/OFF button 32. Instrument 10 actuates prior to release of ON/OFFbutton 32. Immediately after the instrument 10 is turned on, it performs400 a power-on system integrity test and a battery voltage test. If thebattery 86 voltage is below 4.5 volts, a battery low warning (batteryicon on LCD 76) is displayed. If the battery 86 voltage is below 4.2volts, the instrument 10 will not turn on 402. Following being turnedon, all segments of the display 76, including all icons, are displayed404 for 2 seconds. If it is enabled, the transducer 80 sounds for thefirst one/half second of this 2 second display check.

After 2 seconds, all segments and icons disappear and the ROM codenumber from key 64 and code icon appear 406 on LCD 76 for 2 seconds,then disappear. During this time, the instrument 10 scales itself usingthe remission of white tile 142. Scaling is followed by the lighting 408of the strip icon, right arrow icon, and flashing blood drop icon. Thisicon display prompts the user to apply blood to the strip 106 and thento insert the dosed strip 106 into the opening 104 provided therefor ininstrument 10.

The user applies blood to the strip 106 and allows it to soak into thestrip mesh until it is fully absorbed. Within two seconds of properinsertion of the strip 106, the instrument 10 deletes the strip icon,blood drop icon and right arrow icon from display 76, and begins thetiming period for the chemistry in the reagent pad of strip 106 to reactwith the medically significant component, glucose in this example, ofthe applied blood. Within two seconds of insertion of the strip 106, thedisplay 76 sequentially displays 410 (in clockwise rotation) thequadrants on the error or "X" display at a rate of one segment per halfsecond. No timing need be displayed on the instrument 10's LCD 76because of the employment of an endpoint chemistry on strips 106. Whenthe strip 106's reaction is determined by the instrument 10 to havereached an endpoint, the instrument 10 beeps once and then displays 412a blood glucose value and the mg/dL icon. The instrument 10 alsodisplays the strip icon and left arrow icon to prompt the user to removethe reacted strip 106. The glucose result is stored in the newest(first) memory location, pushing all previously stored glucose readingsdown one location in memory.

After the strip 106 is removed, the instrument 10 again rescales itselffrom the white tile 142 to ready itself for the next strip 106 reading.The instrument 10 then returns to the dosed strip insertion prompt 408.

The instrument 10 can verify that an unreacted strip 106 is acceptablefor use. It does this by reading the unreacted strip 106 to make surethat its reagent pad remission value is within the specified percentremission limits stored in the code ROM key 64. performance of thischeck is at the user's discretion. The instrument 10 is capable ofperforming 410, 414 this check when the instrument is prompting 408 fora dosed strip or during 408, 416, 408, 410, 414 a memory recall display.

To perform this strip 106 integrity check, the user removes an unreactedstrip 106 from the vial containing such strips and inserts the unreactedstrip 106 into the instrument 10's slot 104 with the reagent pad facingthe optics. Within two seconds after a strip 106 has been inserted, theinstrument 10 detects the presence of a strip 106 and begins 410 itstiming display. During this display, the user must depress 416 thememory button 50 once. This causes the instrument 10 to perform thestrip 106 integrity check. After the memory button 50 has been pressed,the instrument 10 will read the strip 106's remission and compare thestrip 106's remission against the programmed limits that have beenprovided by the lot specific ROM key 64.

Strip 106 integrity approval is signaled through the strip removalprompt 414 and a single beep. Strip 106 approval permits the user toproceed with a test on a reacted strip 106 by prompting 408 for a dosedstrip after the unreacted strip 106 is removed.

Strip integrity errors are signaled 418, 420 through the display of theflashing error ("X") icon, flashing strip icon and three beeps. Theinstrument 10 remains in this display state until the bad strip 106 isremoved. After strip 106's removal, the instrument 10 prompts 408 for adosed strip.

Glucose test values are stored automatically after every test using"first (oldest) in, first deleted" and "last (newest) in, firstrecalled" protocols. Once the memory has filled to its thirty readingcapacity, each new reading added causes the oldest reading to be deletedfrom memory.

Memory recall mode 416 is accessible from the dosed strip prompt 408.Memory recall function is initiated by pushing the memory button 50once. This displays the first memory location (1).

After one second, the display changes 422 to display the contents (aglucose reading) of the selected memory location. The display reverts416 to the memory location display (1 in this example) after 4 seconds.If no button is pushed, the cycle of memory location 416 and memorylocation contents 422 continues to repeat itself for 5 minutes beforethe instrument 10 turns itself Off. The memory display cycle can also beterminated by the insertion 416, 422, 408 of a test strip 106 into theinstrument 10. Recall of the remaining values from memory isaccomplished by pressing 408, 416 the memory button 50 over and overagain until all thirty stored values and their memory locations havebeen displayed. Each time the memory button 50 is depressed, the nextmemory location is displayed. Memory locations and results cycle tolocation 1 once the user advances beyond the oldest value. If fewer than30 results are stored in memory, the first location (location 1) isdisplayed following the last result stored when the memory is advancedbeyond the last result. The memory icon is displayed 416, 422 at alltimes during memory recall.

If at any point 416, 422 a strip 106 is inserted, the instrument 10reverts 408, 410 to the test/timing mode. Insertion of a strip 106(reacted or unreacted) automatically causes the instrument 10 to revertto this mode and resets memory to the first (newest) location.

The instrument 10 uses the code ROM key 64 as follows: With theinstrument 10 off, the user removes the old ROM key 64 from theinstrument 10 and discards it. A new ROM key 64 is packaged in everysupply of strips 106. The user inserts the new ROM key 64 containinginformation pertinent to the new supply of strips 106 into the keyhousing portion 18 on the instrument 10 prior to turning the instrument10 on. When the instrument 10 is turned on, the instrument 10 checks theintegrity of the data contained in ROM key 64 via a checksum method. Ifthe ROM key 64 data is found to be questionable, then a code error isdisplayed 424. During the performance 410 of a test, prior to thecalculation 412 of a new glucose result, the instrument 10 checks theROM key 64 to see if it has been changed. If the ROM key 64 has beenchanged since the instrument 10 was turned on, a code error is displayed424. The instrument 10 remains in this display until it either timesitself off (5 minutes), or is turned off.

When test results exceed the upper limit contained in the ROM key 64,then the message HI is displayed in place of a numeric result. If theresult does not exceed the lower limit contained in the ROM key 64, LOappears on the display The mg/dL icon is displayed in both cases.

Instrument 10 verifies the remission of its white tile 142 and signifiesa dirty tile 142 by displaying 426 CLE (for "clean") on display 76. Theinstrument 10 does not permit the user to begin a testing procedure ormemory recall from this display. The only remedy for this error is toturn the instrument 10 off. This error occurs if the slope calculated406 from the remission of the white tile 142 is not within instrument10's internal slope limits, typically +5% to -10% of its target value.This error also occurs if the instrument 10 is turned on with a strip106 inserted in it.

The instrument 10 shuts itself off automatically 5 minutes after thelast button push or strip 106 insertion. Automatic shut off occursregardless of instrument 10 mode or the last button pressed. DepressingON/OFF button 32 while the instrument 10 is on turns the instrument 10off.

Transducer 80 provides an audible beep: when the instrument 10 is turnedon (0.5 second); when a strip 106 is inserted into opening 104 (0.25second); whenever an error message is displayed (three times for 0.1second each); at the end of a test to indicate that a result isdisplayed or an unreacted strip 106 is usable (0.25 second); and,whenever either button 32 or button 50 is depressed as a "key click"sound (two cycle duration). Transducer 80 actuation can beenabled/disabled by the simultaneous actuation of both ON/OFF button 32and memory button 50 as the instrument 10 is turned on.

The instrument 10 denotes errors by displaying 428 the "X" icon incombination with an error message or other icon. There are two errortypes: recoverable and non-recoverable. Strip errors are correctable byremoval of the strip 106 from the instrument 10. All other errors arenon-recoverable and require the instrument 10 to be turned off in orderto clear the error.

The following errors are recoverable strip errors. Removal of the stripwill cause the instrument 10 to return to the dosed strip prompt 408:the Bad Strip error 418, caused by an improperly reacted strip 106 or astrip 106 which is degraded in any way as to make its stateindeterminable: and the Strip in Backwards error 420, caused by thestrip 106 being inserted with its blood application side toward theinstrument 10's optics.

The following errors are non-recoverable, as they are the results ofinstrument measurement problems: the Dirty Optics error 426, whichoccurs if the instrument 10's white tile 142 is dirty or degraded, or ifthe instrument 10 is turned on with a strip 106 already inserted in it;the Electronics Fault error 402, which is caused by the detection of afault during the instrument 10's power-on self-test or during adiagnostic check; the Strip Removed During Test error 428, which iscaused by removing a strip 106 during the performance of a test so thatinstrument 10 is unable to complete the test cycle; and, the Codingerror 424, which is caused by the detection of a code ROM key 64 readerror or a mismatch of the lot code number read when instrument 10 isturned on with the lot code number read just prior to the calculation ofa glucose result. The only remedy for these errors is to turn theinstrument 10 off.

The instrument 10 provides certain prompt messages to the user,including: the Strip Removal prompt, by which the instrument prompts theuser to remove a strip 106 by displaying the strip icon and left arrow(<) icon; and the Dosed Strip prompt, by which the instrument 10 promptsthe user to insert a dosed strip 106 by displaying the strip icon, rightarrow (>) icon, and flashing the blood drop icon. Flashing segments oricons in any mode of operation are displayed for 0.5 second and off for0.5 second.

In addition to its normal operating mode for determining the remissionsof reacted test strips, the instrument 10 has a diagnostic softwarepackage that is accessed via installation of a special diagnostic ROMcode key 64. The diagnostic ROM code key 64 is installed in key housingportion 18 before the instrument 10 is turned on. Once the instrument 10is turned on with the diagnostic ROM code key installed, the followingfunctions are accessible instead of the normal operating modes.

Once instrument 10 is turned on in the diagnostic mode, instrument 10enters the check strip diagnostic 430. The instrument displays dl in theglucose value field, or results field, for one second. After one secondthe instrument 10 additionally displays the strip icon and right arrowicon to prompt the operator to insert a check strip 106 provided withthe diagnostic code ROM key 64. If the user presses memory button 50during this display, the instrument 10 advances to the next diagnostictest 430.

Upon insertion 430 of the check strip, the instrument 10 measures theremission of the check strip and compares this remission to a targetremission value range stored in the diagnostic code ROM key 64. If themeasured remission agrees with the target value range then the resultsfield of the display 76 is blank, transducer 80 beeps once and the useris then prompted 432 to remove the check strip by turning off the rightarrow icon, and turning on the left arrow icon while continuing todisplay the strip icon.

Upon removal of the check strip from the instrument 10 after asuccessful check, the instrument 10 returns 430 to the start of thecheck strip diagnostic routine and remains in this routine until theinstrument 10 is turned off, or until the user advances to the nextdiagnostic routine by pressing the memory button 50.

If the measured remission of the check strip does not match 434 thetarget value in the diagnostic code ROM key 64, the instrument 10 beepsthree times, CLE flashes in the results field on display 76, and theerror icon "X" is displayed. The only way to exit this display is toturn instrument 10 off.

If the user advances past the first diagnostic check 430 by pressingmemory button 50, then the IR (infrared) sensor check is prompted 436 bydisplaying d2 in the results field. After one second, the instrument 10checks for the presence of a strip in the instrument by using thereagent pad detector. If the instrument 10 determines 440 that a strip106 is in the instrument 10, it prompts the user to remove the strip bydisplaying the strip icon and left arrow icon until the strip isremoved.

If the instrument 10 detects 442 no strip, the instrument 10 then readsthe IR detector 266. If the IR detector 266 reads a remission valueinconsistent with an empty strip carrier 120, 134, then instrument 10displays OFF 444 in the results field of display 76 to signify that theIR detector 266 is sensing a strip 106 when none is present. Thisdisplay will remain until the instrument 10 is turned off.

If the instrument 10 determines 436, 442 that no strip 106 is presentand that the IR detector 266 sees no strip 106, then it prompts 442 theuser to insert a strip 106 by displaying the strip icon and right arrowicon until a strip 106 is detected by the reagent pad detector 300. Oncea strip 106 is sensed by the reagent pad detector 300, the stripdetector 266 is measured. If this measurement is inconsistent with thepresence of a strip 106 in the instrument 10, then the instrument 10beeps three times, the display field displays OFF 442, 444 and the errorX icon flashing until instrument 10 is turned off.

If the IR detector 266 senses 436, 440 the presence of a strip 106 inthe instrument 10, then the results field of display 76 is blank, andthe user is prompted 440 to remove the strip 106 by displaying of thestrip icon and left arrow icon. Once the strip 106 is removed, thedisplay 76 returns to the d2 display until the user advances to the nextdiagnostic check 446 by pressing memory button 50 or until instrument 10is turned off.

If the user advances past the customer control strip diagnostic 430 andpast the IR sensor 266 check 436 by using memory button 50, then thedisplay check 446 will be prompted by displaying d3 in the results fieldfor one second. After one second, all segments of the display 76 will bedisplayed for five seconds. Display 76 then alternates between the d3display and the all segments display until the user advances to the nextdiagnostic check 450 by pressing memory button 50 or until instrument 10is turned off.

If the user advances past the first three diagnostic checks 430, 436,446 by using memory button 50, then the d4 prompt for the transducer 80check 450 will be displayed in the results field. After one second,transducer 80 beeps for two seconds regardless of whether the user hastransducer 80 switched off or not. After transducer 80 has beeped fortwo seconds, it will turn off for one second and then on for two secondsand so on, until the user advances to the next diagnostic check 454 bypressing memory button 50 or until the instrument 10 is turned off.

If the user advances past the first four diagnostic checks 430, 436,446, 450 using memory button 50, then instrument 10 enters the batterycheck 454 and prompts the user by displaying d5 in the results field,and displaying the battery icon. At the end of one second, theinstrument 10 repeats its power-on battery check 400.

The instrument 10 displays a number based on the following calculation:##EQU1## Of course, numbers of less than 100 are displayed if thebattery icon was being displayed prior to entering 454 the d5diagnostic.

This display will remain on until the user returns a to the firstdiagnostic check, d1, by pressing memory button 50 or until instrument10 is turned off.

The operation of certain software functions of the disclosed instrumentmay be better understood by reference to the attached source listing forμC 200 and illustrative data stored in the EEPROM of a typical key 64.In the source listing, CRD or Chemistry Remission Difference is theamount of remission difference which a delta must be less than in orderto reach the end of reaction (EOR). CRD is a 12 bit number in bank 1 RAMwhich is an input to the function REACTION. The format of CRD is a 12bit binary remission multiplied by forty.

IWMI is an 8 bit number in bank 1 RAM which is an input to functionREACTION which determines the number of half second increments of timeto delay before taking the first remission. IWMI is allowed to be from 0to 255. If IWMI equals 0, then no delay will occur. If it equals 1 thenone half second of delay will occur, and so on.

TINC is an 8 bit number in bank 1 RAM. TINC is an input to the functionREACTION which determines the number of half second increments of timewhich will elapse between successive remission readings. TINC ispermitted to be from 0 to 255. If it is 0, then one half-secondincrement of time will elapse. If it is 1, then two half-secondincrements will elapse, and so on.

NPS is an input to the function REACTION which is a 4 bit number in bank1 RAM. NPS represents the number of remission readings that will betaken between comparisons. It is allowed to be from 1 to 6. If NPS=1,then one remission reading is taken between those which are compared,and so on.

NPSA is an 8 bit number in bank 1 RAM which is an input to functionREACTION. NPSA is a function of NPS. NPSA essentially contains the sameinformation as NPS but in a form which is more easily used by theprocessor It is defined as:

    NPSA=(NPS+1) * 8

IWMA is an 8 bit bank 1 RAM number. IWMA is an input to functionREACTION. IWMA controls the number of comparisons that the EOR portionof the algorithm will make before it terminates. IWMA is permitted to befrom 1 to 255. If IWMA equals 1, then only one comparison will be made.If IWMA equals 2, then a maximum of two will be made, and so on.

ERS is a 1 bit number in bank 1 RAM which is an input to functionREACTION. ERS causes the MAX₋₋ F flag to be set if the function REACTIONreaches EOR by reaching IWMA.

EORREM 1 is a 32 bit floating point number in bank 1 RAM which Containsthe last remission taken by function REACTION. EORREM 1 is an output offunction REACTION.

EORCOUNT is an 8 bit bank 1 RAM number which contains the number ofcomparisons done during EOR. It will never equal 0. It will always befrom 1 to 255. EORCOUNT is an output of function REACTION.

MAX₋₋ F is an output of function REACTION. MAX₋₋ F is a 1 bit bank 1 RAMnumber. MAX₋₋ F is set equal to 1 if EOR is reached by the number ofcomparisons equalling IWMA and ERS is also 1. If these conditions arenot met, then MAX₋₋ F is cleared to zero.

TRACE₋₋ F is a 1 bit bank 0 (zero) RAM input to module REACTION whichindicates that the meter is in TRACE MODE. In TRACE MODE, all remissionreadings are sent out the I/O port.

SE₋₋ F is a 1 bit bank 1 RAM number which is an put. If SE₋₋ F is set, astrip error has occurred. out Two conditions can cause this: (1) EORREM1 less than COL or greater than COH; or (2) EOR reached by finding adelta less than CRD, but the last 2 remissions taken did not have deltasless than CRD.

COL is a bank 1 RAM location. Its format is a 12 bit binary remissionmultiplied by 40. All EORREM 1 values found by this function arecompared to this number. If EORREM 1 is less than COL, then SE₋₋ F isset.

COH is a bank 1 RAM location. The format is a 12 bit binary remissiontimes 40. All EORREM 1 values found by this function are compared tothis number. If EORREM 1 is greater than COH, then SE₋₋ F is set.

REACTION ASSESSMENT Summary

Reaction Assessment is responsible for observing the strip adaptor anddetermining when the remission of the object in the strip adapter hasreached the EOR. It does this by periodically taking full powerchemistry pad remissions and analyzing these against parameters found inthe external ROM. The final remission is placed in a reserved locationin RAM. In addition, Reaction Assessment determines how many comparisonswere made during the search for EOR. During the operation of thismodule, a rotating arrowhead is displayed on the LCD display as a meansof indicating that this module is operating. This module also transmitsthe value of each remission taken out the serial port if TRACE₋₋ F isset. If the MEM button is pushed during the execution of this module,then control passes to the STRIP INTEGRITY module and ReactionAssessment is aborted.

More Detailed Explanation

This function is responsible for observing the strip adapter anddetermining when EOR occurs or if the MEM button is pushed. In addition,Reaction Assessment displays a rotating arrow on the LCD as a means ofproviding a visual indication that the meter is busy. It also outputseach remission taken if TRACE₋₋ F is set.

Reaction Assessment begins by clearing the LCD and darkening a singlearrowhead. The first arrowhead darkened is not specified and will varyindeterminately. For the duration of the execution of this function theLCD will change its display every half second. The display will changeby lightening the arrowhead that is currently dark and darkening thearrowhead which is adjacent to it in the clockwise direction. At thecompletion of this function the duration of time since the LCD displaywas changed will be between approximately 20 and 300 msec. A typicaltime will be around 100 msec. This duration varies with the timerequired to take a remission and whether TRACE₋₋ F is set or not. It isintended that if a continuation of the rotating arrowhead display isdesired following the completion of this function, then it is necessaryto wait another half second before changing the LCD display In addition,SE₋₋ F is cleared at this time.

Reaction Assessment employs the power conservation module so that whenit is not actively taking remission readings or doing calculations itputs the meter in a power conservation mode which minimizes powerconsumption yet still permits the meter to respond immediately to anyevent which can cause a termination of power savings.

The second thing that this function does is to examine RAM location IWMIto determine the amount of initial delay before taking the firstremission reading. IWMI is an 8 bit binary integer. Each count of IWMIrepresents a half second of delay. IWMI may be from 0 to 255. 0 impliesno delay and 255 implies 255 half seconds of delay. An example of IWMIis illustrated in FIG. 11. Here, IWMI has a value of 3. This causes 1.5seconds of delay from the start of this function to where the firstremission is taken.

Once the requirements of IWMI have been met, then a single, full powerremission is taken on the chemistry channel. This remission is referredto as the first remission reading.

The next task that the function REACTION performs is a TRACE CHECK. Thisinvolves checking the 1 bit RAM location TRACE F. If this location holdsa 0, nothing happens. If it holds a 1, then the remission just taken issent out the serial port as a 4 byte floating point number (leastsignificant byte first) in the PC communication format.

The EOR portion of this function is conducted at this time. To reachEOR, one of two events must occur. Either a comparison of two remissionsis found to have a change, or delta, which is less than CRD, or atime-out occurs after a number of comparisons equal to IWMA has beenmade.

End of Reaction by achieving a DELTA<CRD

CRD is a number found in RAM which is a limit for how small delta mustbe in order to constitute EOR. Delta is the result of subtracting themost recent remission from a prior remission determined by ROM code key64 parameter NPS. The comparison between CRD and a delta is made asfollows:

    Is |delta|<|CRD|?

If the answer to this question is yes, then EOR has been reached. Ifnot, then another comparison must be made.

The timing for these events can best be described in connection withFIG. 11. The first remission reading has already been taken (time=1.5sec.). The amount of delay until a subsequent remission reading is takenis controlled by TINC If TINC equals 0, then the delay increment will beone half second. If TINC equals 1, then 2 increments of one half secondwill occur. TINC is permitted to vary from 0 to 255, so it will providedelays of from 0.5 to 128 seconds. The example in FIG. 11 shows a TINCof 1 which causes a delay of two one half second increments betweenremission readings.

A delta is formed by comparing two remission readings. The tworemissions compared are determined by RAM locations NPS and NPSA.NPSA=(NPS+1)*8. NPS refers to how many previous remissions will beskipped before using a remission to form a delta. If NPS equals 1, as inthe example of FIG. 11, then one remission is skipped. For this example,the first delta is calculated after the third remission reading istaken. The delta is calculated by subtracting the first remissionreading from the third remission reading. NPS is permitted to be from 0to 6, permitting from 0 to 6 remission reading to be skipped betweencomparisons. If, for example, NPS=6, six remission readings are skipped,and the remission reading which was detected seven remission readingsago is the one that is used to calculate delta.

RAM location EORCOUNT is used to keep track of how many comparisons aremade during this function. At the beginning of this function, EORCOUNTis set equal to zero. RAM location EORCOUNT is incremented by 1 eachtime a comparison is made until a delta less than CRD is found. If adelta is found that is less than CRD, then the software decides that EORhas been reached. In the example provided in FIG. 11, a delta less thanCRD was reached when the fourth reading was taken. Therefore, the finalEORCOUNT value for this example is 2.

Once the EOR is reached by finding a delta less than CRD, one moreremission reading is taken after a time interval controlled by TINC.Following this remission, a Trace Check remission is read. This TraceCheck remission is also compared to a previous remission controlled byNPSA. EORCOUNT is not incremented when this remission is read and itscorresponding delta is calculated. If this delta is less than CRD, thenthe remission just taken will be stored at RAM location EORREM1. Thesoftware will then continue as described following the next paragraph.If this delta is not less than CRD, then the meter will continue asdescribed in the next paragraph. FIG. 11 does not illustrate thiscondition since the fifth reading is quite low and the delta (THIRDDELTA) created thereby is greater than CRD. However, if THIRD DELTA hadbeen less than CRD, then the fifth reading would have been the last andwould illustrate this condition.

The meter next takes another remission reading immediately withoutwaiting for TINC. This remission is compared to the same remission as isthe remission taken after delta less than CRD. The example in FIG. 11shows a delta being created between the third reading and the sixthreading. If the delta is not less than CRD, then the 1 bit RAM locationSE₋₋ F is set. EORCOUNT is not incremented when this remission is readand its corresponding delta is calculated. This remission is stored atRAM location EORREM1. A Trace Check is performed. The function nowproceeds as described below.

Each time a comparison is made, the RAM location EORCOUNT is incrementedby 1. EORCOUNT is zeroed at the beginning of this function. If so manycomparisons are made that EORCOUNT equals IWMA, then EOR will have beenreached. If this happens, and if the 4 bit RAM location ERS equals 1,then the 1 bit RAM location MAX₋₋ F is set. Otherwise MAX₋₋ F is clearedby this function, regardless of how this function terminates. An exampleof this type of EOR is given in FIG. 12. Here, IWMA equals 5. After fivecomparisons (deltas) are calculated and none of these deltas are foundto be less than CRD, EOR is reached.

Once EOR has been found by reaching IWMA, then another remission istaken after TINC has elapsed. Following this remission, a Trace Checkremission is read immediately. This remission is then written into RAMlocation EORREM1.

Regardless of how EOR was reached, this function now proceeds byoutputing 4 bytes of EEH if the TRACE₋₋ F is set. This indicates to a PCthat the function REACTION is completed.

The last thing REACTION does is to check if the EORREM1 value is greaterthan RAM number COL and less than RAM number COH. If EORREM1 is notbetween COL and COH then the SE₋₋ F bit in RAM is set. If EORREM1 isbetween COL and COH then the SE₋₋ F bit is not modified. It is possiblethat EOR was reached by finding a delta less than CRD, and that the lasttwo remissions did not meet the CRD requirements but the last remissionwas within the limits set by COL and COH. In this case, a strip error isstill considered to have occurred, and the SE₋₋ F bit remains set.

Throughout this entire function, the meter is alert for a pressing ofthe MEM button. If the MEM button is pressed, then a branch to the STRIPINTEGRITY function is performed. This terminates the Reaction Assessmentfunction.

What is claimed is:
 1. Apparatus for determining the remission of achemistry which reacts with a medically significant component of a bodyfluid, the remission of the chemistry changing as it reacts, theapparatus comprising a source of radiation for irradiating thechemistry, a remission detector for detecting remissions of radiationfrom the chemistry, means for providing a radiation pathway between thesource and the chemistry, means for providing a remission pathwaybetween the chemistry and the remission detector, and means fordetermining the rate of change of remission of the chemistry withrespect to time, the rate determining means comprising means forinitially stimulating the radiation source at a first time rate, forreceiving remission data from the remission detector, for comparingremission data from remission measurements spaced apart by a firstnumber of intervening remission measurements, for determining when thedifference between compared data exceeds a first predetermined limit,for changing the time rate of stimulation of the radiation source to asecond and greater rate of stimulation per unit time once the differencebetween compared data exceeds the first limit, for comparing remissiondata from remission measurements spaced apart by a second number ofintervening remission measurements, which second number may be the sameas, or different from, the first number, for determining when thedifference between compared data no longer exceeds a secondpredetermined limit, and for converting remission data identified basedupon determining when the difference between compared data no longerexceeds the second limit to the concentration of the medicallysignificant component of the body fluid, and means for coupling theradiation source and remission detector to the rate determining means.2. The apparatus of claim 1 wherein the remission detector comprises aradiation sensitive device, and further comprising a capacitor forproviding a first current flow through the radiation sensitive device inresponse to detection of remission, the first current flow dischargingthe capacitor from a known, initial, charged condition, and a constantcurrent source for recharging the capacitor to the known, initial,charged condition when the first current flow terminates.
 3. Theapparatus of claim 2 wherein the rate determining means comprises a timebase generator, means for measuring the time interval required for theconstant current source to recharge the capacitor to the known, initial,charged condition, and means for coupling the time interval measuringmeans to the time base generator.
 4. The apparatus of claim 1 comprisinga substrate for supporting the chemistry, a device for accepting thesubstrate, the device defining the pathway along which radiation isguided from the radiation source to the chemistry when the substrate isinserted into the device and the pathway along which remission is guidedfrom the chemistry to the remission detector when the substrate isinserted into the device, a remission standard, means for movablysupporting the remission standard to permit it to move from a positionin which it receives radiation from the radiation source and produces astandard remission which is guided along the pathway to the remissiondetector when no substrate is inserted into the device to a positionseparated from the radiation source by the substrate when the substrateis inserted into the device.
 5. The apparatus of claim 4 wherein themeans for movably supporting the remission standard further comprisesmeans for supporting the radiation source, the pathway along whichradiation is guided from the source to the chemistry when the substrateis inserted into the device including a first slot formed opposite thechemistry when a substrate is inserted into the device, the first slotbeing located adjacent the means for supporting the radiation source fordirecting radiation therefrom onto the chemistry when a substrate isinserted into the device.
 6. The apparatus of claim 5 wherein thepathway along which remission is guided from the chemistry to theremission detector when a substrate is inserted into the device alsoincludes the first slot.
 7. The apparatus of claim 6 wherein the meansfor movably supporting the remission standard includes a first surface,the pathway along which remission is guided from the chemistry to theremission detector when a substrate is inserted into the deviceincluding a second slot formed in the first surface adjacent the firstslot.
 8. The apparatus of claim 7 wherein the means for movablysupporting the remission standard includes a second surface lying at anonzero angle to the first surface, the pathway along which radiation isguided from the source to the chemistry when the substrate is insertedinto the device including a third slot formed in the second surface. 9.The apparatus of claim 8 wherein the third slot lies between the sourceand the chemistry when the substrate is inserted into the device. 10.The apparatus of claim 9 wherein the first slot lies between the thirdslot and the chemistry when the substrate is inserted into the device.11. The apparatus of claim 10 wherein the first slot lies between thechemistry and the remission detector when the substrate is inserted intothe device.
 12. The apparatus of claim 11 wherein the second slot liesbetween the first slot and the remission detector.
 13. The apparatus ofclaim 8 wherein the second surface lies between the means for supportingthe radiation source and the chemistry when the substrate is properlyinserted into the device.
 14. The apparatus of claim 5 and furthercomprising a second radiation source and a second remission detector,and wherein the means for movably supporting the remission standardfurther includes a first surface which lies adjacent the first slot whenthe substrate is properly inserted into the housing, the first surfacelying adjacent the device, and a second pathway along which radiation isguided from the second radiation source to the substrate when thesubstrate is inserted into the device and along which remission isguided from the substrate to the second remission detector when thesubstrate is inserted into the device.
 15. The apparatus of claim 14 andfurther comprising an instrument for determining the concentration of amedically significant component of a body fluid and for indicating thedetermined concentration of the medically significant component to auser of the instrument, the instrument comprising an instrument case forthe instrument's components including the device, one of theinstrument's components comprising a printed circuit board, at least aportion of the means for movably supporting the remission standard, thefirst-mentioned and second radiation sources and the radiation sourceand the second radiation source and the remission detector and thesecond remission detector being mounted on the printed circuit board.16. A method for determining the remission of a chemistry which reactswith a medically significant component of a body fluid, the remission ofthe chemistry changing as it reacts, the method comprising the steps ofirradiating the chemistry, detecting remissions of radiation from thechemistry, providing a radiation pathway between a radiation source andthe chemistry, providing a remission pathway between the chemistry and aremission detector, and determining the rate of change of remission ofthe chemistry with respect to time, the irradiating, remission detectingand rate determining steps together comprising the steps of initiallyirradiating the chemistry at a first time rate and detecting remissionstherefrom, comparing remission data from remission measurements spacedapart by a first number of intervening remission measurements,determining when the difference between composed data exceeds a firstpredetermined limit, changing the time rate of irradiation of thechemistry to a second and greater rate of irradiation per unit time oncethe difference between compared data exceeds the first limit, comparingremission data from remission measurements spaced apart by a secondnumber of intervening remission measurements, which second number may bethe same as, or different from, the first number, determining when thedifference between compared data no longer exceeds a secondpredetermined limit, and converting remission data identified based upondetermining when the difference between compared data no longer exceedsa second predetermined limit to the concentration of the medicallysignificant component of the body fluid.
 17. The method of claim 16 andfurther comprising the step of providing a first current flow through aradiation sensitive device in response to detection of remission, thefirst current flow discharging a capacitor from a known, initial,charged condition, and providing a constant current for recharging thecapacitor to the known, initial, charged condition when the firstcurrent flow terminates.
 18. The method of claim 17, the ratedetermining step comprising the steps of generating a time base, andmeasuring the time interval required for the constant current torecharge the capacitor to the known, initial, charged condition.
 19. Themethod of claim 16 comprising the steps of supporting the chemistry on asubstrate, accepting the substrate in a device providing the pathwayalong which radiation is guided from the radiation source to thechemistry when the substrate is inserted into the device and along whichremission is guided from the chemistry to the remission detector whenthe substrate is inserted into the device, providing a remissionstandard, and movably supporting the remission standard to permit it tomove from a position in which it receives radiation from the radiationsource and produces a standard remission which is guided along thepathway to the remission detector when no substrate is inserted into thedevice to a position separated from the radiation source by thesubstrate when the substrate is inserted into the device.
 20. The methodof claim 19 and further comprising irradiating the substrate with asecond radiation source and detecting remissions from the substrate witha second remission detector, and providing a second pathway along whichradiation is guided from the second radiation source to the substratewhen the substrate is inserted into the device and along which remissionis guided from the substrate to the second remission detector when thesubstrate is inserted into the device.
 21. The method of claim 20 andfurther comprising the steps of providing an instrument for determiningthe concentration of a medically significant component of a body fluidand for indicating the determined concentration of the medicallysignificant component to a user of the instrument, providing in theinstrument a printed circuit board for mounting at least a portion ofthe remission standard, the radiation source and the second radiationsource and the remission detector and the second remission detector. 22.The method of claim 20 wherein the steps of detecting the remissionsdetected by the remission detector and the second remission detectorcomprise the steps of detecting the remissions detected by the remissiondetector and the second remission detector substantially simultaneously.23. The method of claim 16 wherein the steps of initially irradiatingthe chemistry at a first time rate, comparing remission data fromremission measurements spaced apart by a first number of interveningremission measurements, determining when the difference between compareddata exceeds a first predetermined limit, and determining when thedifference between compared data no longer exceeds a secondpredetermined limit together comprise the steps of retrieving datarepresentative of the first time rate, the first number of interveningremission measurements, the first predetermined limit, and the secondpredetermined limit from a read only memory (ROM), and furthercomprising the step of retrieving from the ROM data representative of aconversion parameter for converting the remission data identified basedupon determining when the difference between compared data no longerexceeds the second limit to the concentration.
 24. The method of claim23 and further comprising the steps of providing an instrument fordetermining the concentration of a medically significant component of abody fluid and for indicating the determined concentration of themedically significant component to a user of the instrument, providingthe ROM on a key, providing on the instrument a socket for receiving thekey, insertion of the key into the socket coupling the ROM to theinstrument and permitting access by the instrument to the datarepresentative of the first time rate, the first number of interveningremission measurements, the first predetermined limit, the secondpredetermined limit, and the conversion parameter.